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Swapping germs with the dog

Here’s yet another reason to wash your hands after playing with the dog: Researchers in Europe have uncovered a new piece of evidence suggesting noroviruses, the group of bugs often responsible for what’s known as “stomach flu,” can be transmitted from pet dogs to humans.

This tidbit of information appears in the current issue of the Journal of Clinical Virology (thanks to barfblog, a food safety blog published by Doug Powell of Kansas State University, for the heads up) and it’s worth a glance by anyone who lives with a dog or has frequent contact with dogs.

Noroviruses, as many folks already know, are among the most common causes of gastroenteritis, which is characterized by acute vomiting, diarrhea and stomach cramps. The virus is typically spread through contaminated food or drink, direct contact with someone who’s sick, or hand-to-mouth contact with a surface – a countertop, for instance – that’s contaminated with the virus.

Apparently we might need to include canine companions in this equation. A group of Finnish researchers analyzed 92 fecal samples from indoor pet dogs, using illness in the household as their criterion – either one of the humans or dogs in the home had to have vomiting or diarrhea in order to be considered for the study.

The analysis revealed the presence of human norovirus in four of the dogs who’d had direct contact with a human showing symptoms of the virus. The researchers also found that three of the four samples contained a norovirus with the same genotype, GII, that is one of the most common strains to infect humans.

The researchers wrote, “Our results suggest that HuNoVs can survive in the canine gastrointestinal tract. Whether these viruses can replicate in dogs remains unresolved, but an association of pet dogs playing a role in transmission of NoVs that infect humans is obvious.”

Studies on norovirus strains among dogs have been few and far between. A Portuguese team analyzed stool samples from 105 dogs at shelters, veterinary clinics and pet stores and reported in a paper, published in 2010 in the Emerging Infectious Diseases journal, that 40 percent of the samples that came from dogs with diarrhea tested positive for a novel form of norovirus.

Another study, this one conducted in Italy, put the overall prevalence of norovirus among dogs at around 2 percent and noted that it may be possible, under certain circumstances, for the virus to be transmitted to people.

More research obviously needs to take place before a definitive link can be established. The ability of dogs and humans to swap pathogens is not surprising, however. About a year ago, another study found several documented cases of human infectious diseases ranging from hantavirus to plague that reportedly were transmitted by household dogs and cats who slept with their human companions.

Most of us with companion animals are devoted to our pets and aren’t about to give them up. The risk of animal-to-human, or zoonotic, disease just comes with the territory. If anything, however, the emerging knowledge about norovirus in dogs underscores that disease transmission is a clear possibility and that hand-washing, sanitation and attention to overall pet health can be a dog owner’s best friend.